<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .w{
            width: 500px;
            height: 500px;
            background-color: #a1a11a;
            margin: 0 auto;
        }
        .w div{
            width: 100px;
            height: 100px;
        }
        .son1{
            background: #f5f5f5;
            position: absolute;
            top: 0;
            left: 0;
        }
        .son2{
            background: pink;
        }
        .son3{
            background: blue;
        }
    </style>
</head>
<body>
    <div class="w">
        <div class="son1"></div>
        <div class="son2"></div>
        <div class="son3"></div>
    </div>
</body>
</html>